Free ink pens are known that have an ink reservoir connected to a writing tip. Controlling the pressure and the leaktightness of such reservoirs under all circumstances (as the ink is used up or in extreme conditions such as onboard an airplane, at high altitude, at high temperatures, etc.), in particular under conditions that might lead to ink leaking via the writing tip, is a recurrent problem, and no known system is fully satisfactory.
For example, a baffle device is known (also known as a deflector or a labyrinth device) for controlling pressure in the reservoir. Depending on the pressure in the reservoir, the baffle device can become saturated with ink or can become emptied of ink so as to match the pressure inside the reservoir with the outside pressure, with this happening both while ink is being consumed and as a result of accidental pressure variations, while still feeding the writing tip with ink.
However, the baffle device on its own, as is to be found in most conventional pens, is not satisfactory: it operates essentially as a buffer having a vent connected to the outside and capable of storing a limited quantity of ink. Thus, if the ink reservoir is subjected to excessive overpressure, the buffer capacity offered by the baffle device can be insufficient and the pen can leak, e.g. via the vent of the baffle device. Conversely, if the pressure inside the reservoir is lower than outside, situations can arise in which the baffle device no longer manages to prevent the feed of ink to the writing tip being interrupted. There exists a need for a novel type of device for controlling pressure for free ink pens.